1. Field of the Invention
The present invention relates to the field of carpet and the manufacture thereof, and more particularly relates to methods of treating carpet to enhance its liquid barrier properties. The invention also relates to carpets with improved liquid barrier properties.
2. Description of Related Art
The majority of carpet is constructed in the following general manner. Carpet pile yarn is first inserted through a primary backing fabric to form tufts of yarn projecting from the surface of the primary fabric. This side is known as the pile side. Backstitches of the yarn protrude through the opposite side of the primary backing to hold the yarn in place. This side is referred to as the underside or back stitch side. The primary backing thus is perforated with many holes during this tufting operation. The carpet is then dyed. Then a coating layer is applied to the underside of the primary backing layer. The coating layer usually includes polymeric latex to lock the yarn tufts in place and to provide an adhesive for a secondary backing fabric. The latex-coated primary backing is then bonded to the secondary backing to form a laminated backing structure.
Additional steps have been added to the process to attempt to enhance repellency and stain resistance of the carpet. For example, it is now a common practice to topically apply to the pile side of the carpet a compound from the class of chemicals known as fluorochemicals. The purpose of applying such fluorochemicals is to reduce the tendency of soil, oil and/or water to adhere to the carpet fibers. It is also a common practice to apply a stain resist compound to carpet, generally nylon carpet, to make the nylon carpet fibers resistant to staining, particularly by anionic or “acid” dyes.
Generally, fluorochemicals are topically applied to carpet after the dyeing step. One conventional method of application is to form an aqueous dispersion of the fluorochemical and then spray that dispersion on the top face (pile side) of the carpet. Another method is to make aqueous-based foam containing the fluorochemical and then apply the foam to the top face of the carpet. See, e.g., U.S. Pat. No. 5,853,814. In both methods, heat is usually applied to drive off excess water and to fix the fluorochemical to the carpet fibers.
Typically, stain resist compounds are applied to carpet from a bath after the dyeing step, but before drying. If a stain resist compound is applied to the carpet, then generally a fluorochemical is applied afterwards by a spraying or foaming step as described in the preceding paragraph.
U.S. Pat. Nos. 5,219,620 and 5,366,161 describe methods of applying a foam composition through the primary backing of the fabric for the purpose of treating the pile side of the carpet. The patents indicate that the foam completely and uniformly penetrates through the carpet backing. The foam-applicator is designed to push the foam through the primary backing from the underside, to treat the pile fibers and provide stain resistance, soil protection and repellency thereto. Hence, there is not left any significant amount of the composition of the foam on the underside of the primary backing, and there is not provided a region on the underside of the backing that improves the liquid-barrier as in the present invention.
U.S. Pat. No. 5,520,962 and 5,851,595 to Jones describe improved methods of applying fluorochemicals and optionally stain resist compounds to carpet or carpet yarn. The methods include immersing the carpet or yarn in an aqueous medium have a pH of less than about 3.5 that contains the fluorochemical and optionally a stain resist compound. These methods provide carpets with excellent repellency characteristics.
Even with the methods described in the art, there is still a possibility that water or other liquids spilled on the carpet, can by drawn down through the carpet yarns by a capillary action. In such a case, the liquid can penetrate through the layers of the carpet below the tufted layer. For instance, if water, a water-based liquid, such as a beverage, soft drinks, soda, coffee, urine, or the like, or another type of liquid (e.g., oil-based) is spilled onto the carpet face, it may permeate through the primary and secondary backings and onto the underlying material, such as the carpet underpad and hardwood floors. The underlying material may become stained and deteriorate over a period of time. Mildew may also grow on the backing and underlying material, causing odor problems.
Different approaches have attempted to deal with this problem by reducing the permeability of liquids through the carpet. As discussed above, one method involves applying a fluorochemical or other water-repellent agent onto the face fiber of the carpet during the fiber-forming or carpet-manufacturing process. In such instances, the fluorochemicals serve to reduce the wettability of the fibers in the finished carpet such that a spilled liquid will initially “bead” on the surface of the fiber. However, if the beaded liquid is not promptly removed, it may eventually be absorbed by the fibers and may penetrate through the primary backing.
Another method for attempting to deal with this problem involves mixing fluorochemicals into the latex composition and then coating the primary carpet backing with the fluorochemical-containing latex. U.S. Pat. Nos. 4,579,762; 4,619,853 and 4,643,930, describe coating the underside of the primary backing with a latex containing fluorochemicals mixed therein such that the primary backing is made substantially impervious to water.
Another approach is described in U.S. Pat. No. 5,558,916, which describes a method for making a carpet having a secondary backing which is substantially impervious to liquids. The methods involve applying a repellent finish onto the underside of the secondary backing material. According to the patent, any liquid spilled on the carpet will become entrapped between the face fiber and the secondary backing. Vacuuming, sponging or other appropriate means can then remove the liquids. This method can be disadvantageous because the liquid may penetrate through the primary backing and hence be difficult to remove.
U.S. Pat. No. 5,714,224 describes applying a layer of polyolefin between the latex layer and the secondary backing for the purpose of providing a moisture barrier layer. This method can be disadvantages due to the extra costs involved in materials in forming the extra layer and in the extra processing step involved. Also, there could be delamination problems between the primary and secondary backing. A similar approach, with similar drawbacks, is described in U.S. Pat. No. 5,612,113, where a thin film of a thermoplastic material is adhesively bonded to either the primary or secondary backing.
Although the foregoing methods may be somewhat effective for providing the carpet with water impermeability properties, such methods may restrict the flexibility of the carpet manufacturing operation. In addition, if such carpets also have a secondary backing, latex containing the mixed fluorochemicals may possibly reduce the adhesion between the primary and secondary backings, thus reducing the delamination strength and tuft bind of the carpet. Moreover, addition of the fluorochemical to the adhesive can cause the combination to become frothy, thereby causing application problems. Also, the combination can cause the carpet to become stiffer, causing installation problems for the carpet.
Treatment of the secondary backing, as in the '916 patent, does provide protection for the materials underneath the secondary backing, such as the pad and subfloor. However, the latex layer, which is between the primary and secondary backing, can also wet out (become wet with liquid) from spilled liquids. This could weaken the latex and could lead to delamination between the backing layers. Moreover, liquids can become entrapped in the latex layer in the process of the '916 patent; and it is generally difficult to remove liquids from the latex layer. Moreover, the process of the '916 patent can be difficult to implement in the industry, because carpet-industry coaters are not set up to remove the water load that comes with application of foam to the secondary backing as taught in the '916 patent. This can lead to difficulty in drying and slower line speeds on the coater. Coaters are known to those in the art as a series of pieces of equipment that apply a coating or backing to the primary backing.
In view of the above disadvantages, it would be desirable to have an improved method for making a carpet with improved imperviousness to liquids. Such a method should be easily adapted to current manufacturing processes. It is also desirable to provide a carpet with improved moisture or liquid barrier qualities. The present invention provides such methods and carpet.